fix: ensure exception is available when BackgroundConsumer open stream fails (#357)

* fix: ensure exception is available when BackgroundConsumer open stream fails

* chore: fix coverage

* Address review comments

* revert

* address review feedback

* raise grpc.RpcError instead of GoogleAPICallError

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

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Co-authored-by: Rosie Zou <rosiezou@users.noreply.github.com>
Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
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